1.1 Atomic Structure Part 1 Flashcards Preview

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Flashcards in 1.1 Atomic Structure Part 1 Deck (38)
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1
Q

What is the mass of a proton?

A

1

2
Q

What is the mass of a neutron?

A

1

3
Q

What is the mass of an electron?

A

1/2000

4
Q

What is the charge of a proton?

A

+1

5
Q

What is the charge of a neutron?

A

O

6
Q

What is the charge of an electron?

A

-1

7
Q

What is the atomic number?

A

The number of protons in the nucleus of an atom

8
Q

What is the mass number?

A

The number of protons and neutrons in the nucleus of an atom

9
Q

What is an isotope?

A

Are atoms of the same element (have the same number of protons) with a different number of neutrons

10
Q

Why do isotopes have the same chemical properties?

A

They have the same number and arrangement of outer shell electrons

11
Q

When are posture ions formed?

A

When the atom loses electrons

12
Q

When are negative ions formed?

A

When atoms gain electrons

13
Q

What are the 4 steps in mass spectrometry?

A
  • ionisation
  • acceleration
  • separation of ions
  • detection
14
Q

What are the two ways an atom can be ionised in step one of mass spec.?

A

Electron impact and electrospray ionisation

15
Q

Describe electron impact ionisation

A
  • Sample is injected into spectrometer and vaporised
  • High energy electrons from an electron gun are fired at the sample
  • The high energy electrons knock off an electron from each particle to form positive ions
16
Q

Write the equation for the electron impact ionisation of magnesium

A

Na (g) -> Na+ (g) + e-

g

17
Q

Explain electrospray ionisation

A
  • sample is dissolved in polar solvent
  • injected through a fine hypodermic needle to give a fine mist
  • the tip of the needle is attached to the positive terminal of a high voltage supply
  • particles gain a proton (H+ ion) from the solvent to form positive ions
18
Q

What is the general equation for electrospray ionisation?

A

M(g) + H+ -> MH+ (g)

19
Q

What is important about the mass of the result of electrospray ionisation?

A

Mass is one more than the sample

20
Q

Why is a volatile solvent used in electrospray ionisation?

A

So it can be easily evaporated

21
Q

What does the mass of the ion at the end of mass spec. depend on?

A

The type of ionisation

22
Q

What is the mass of ion in electron impact ionisation?

A

Mass of element / compound

23
Q

What is the mass of the ion at the end of electrospray ionisation?

A

(Mass of element / compound) + 1

24
Q

How are positive ions accelerated in mass spec.?

A

An electric field is applied

25
Q

What does applying an electric field do to the ions in mass spec.?

A
  • accelerates them

- gives them the same kinetic energy

26
Q

What does the velocity that an ion travels in mass spec. Depend on?

A

The mass

27
Q

Which type of ions reach the detector first in mass spec.?

A

Lighter ions

28
Q

Why is the whole spectrometer kept under vacuum?

A
  • to stop unwanted reactions

- only analyse our sample

29
Q

What is the detection part of mass spec.?

A

The detector records the different ions as they arrive

30
Q

How can ions be detected in mass spec.?

A

The positive ion accepts an e-

31
Q

A graph of the results from mass spec has been drawn. The relative atomic mass of Mg is 24.3. Why is there no peak at 24.3?

A

Because isotopes have whole mass numbers, 24.3 is the average

32
Q

Why must the sample be ionised in mass spec.?

A

So it can be accelerated

So it can be detected

33
Q

What is the isotopic mass?

A

The mass of an isotope relative to 1/12th the mass of an atom of carbon-12

34
Q

What is relative atomic mass (Ar)?

A

The weighted average mass of all the isotopes relative to 1/12th the mass of an atom of carbon-12

35
Q

How do you calculate relative atomic mass?

A

(Mass x abundance of each isotope) / total abundance

36
Q

Why is there only two peaks on the graph of mass spectra obtained from electrospray ionisation?

A

It doesn’t cause fragmentation

37
Q

What is electron impact ionisation used for?

A

Identifying unknowns

38
Q

What is electrospray ionisation used for?

A

Finding the Mr of large, delicate molecules such as DNA